Do not impose that blanket rule. Establish the actual lawful source, entitlement and path under the case facts.
Explain the real route
A legitimate joint or company account needs an accurate explanation of rights and transfers. Its presence should not be hidden, and it does not automatically establish that every payment qualifies.
Start with a source-and-path ledger that identifies who owned each account, how the money was lawfully obtained, and every transfer ending in the enterprise. Joint, corporate, and personal accounts can all appear when the rights and transactions are documented accurately; routing every dollar through one personal account is not a legal shortcut. Decide who will own the U.S. company before funds move. Treaty nationality must cover both the investor and enterprise. Direction and development require at least 50 percent ownership or another means of operational control. A substantial sum, committed beyond discretionary recall and placed at commercial risk, must support an operating enterprise with more than marginal capacity. E-2 offers no direct route to a green card.
Hypothetical example: a Magog cabinetmaker plans an American custom-furniture workshop using savings, a documented distribution from her Canadian company, and money in a joint account with her husband. She should collect the share register, distribution resolution, joint-account statements, wires, lease, equipment orders, ownership documents, and operating plan. The truthful three-source trail may work if entitlement and commitment are clear. Passing the same funds through a newly opened personal account would add a transfer without fixing an undocumented source or a refundable commitment.